Re: [Libreoffice] [GSoC] link-time optimization

Am Mon 22 Aug 2011 04:56:31 PM CEST schrieb Jan Holesovsky <kendy@suse.cz>:

> Hi Honza,
>
> So we have some proof-of-concept LTO work pushed to the LibreOffice
> repository - care to have a look & try it how it copes with your changes
> in gcc etc.? ;-)
>
> git clone git://anongit.freedesktop.org/libreoffice/core
> sudo zypper si -d libreoffice-bootstrap
> ./autogen.sh --enable-lto
> make
> make dev-install
>
> More here: http://www.libreoffice.org/get-involved/developers/ , or
> appear on #libreoffice-dev on irc.freenode.net :-)

OK, I will try it on weekend.  Does it work with GCC 4.6?

Honza
> All the best,
> Kendy
>
> On 2011-08-20 at 23:04 +0200, Matúš Kukan wrote:
> > Hello,
> >
> > I created patch, which allows link-time optimization (--enable-lto)
> > for shared libraries, you need at least gcc-4.5 (I'm not checking for
> > version in configure).
> > gcc-4.5 is not really good for lto but I was able to install
> > LibreOffice with lto enabled. I don't know what should I try to test
> > if it is really faster and how much.
> > Building is slower because gcc is compiling sources twice ? or
> > something like that. But real problem is that lto is memory expensive.
> > We could gain more with bigger libraries but it's not possible with
> > gcc-4.5, I'm afraid.
> > Unfortunately I was not able to install gcc-4.6, so I don't know if
> > it's better but it should.
> >
> > You can use gold as linker for elf libraries, it's really faster but
> > linking phase it's not that much.
> > Most of the time is running lto1 executable and it eat cca 2GB RAM
> > when optimizing sw library. (cca 4,5 minutes for me)
> >
> > So it is possible but not in parallel. And not for really big libraries.
> > I am hoping it will be much better with gcc-4.6.
> >
> > ok to push ? For sure there could be better message at least in configure.
> >
> > Best regards,
> >
> > Matúš
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